Rumpfniveauverschiebungen an (110) Oberflächen von Ir, Pt und Au

Dückers, K.

Book/Report

FZJ-2018-02898

Rumpfniveauverschiebungen an (110) Oberflächen von Ir, Pt und Au

Dückers, K. (Corresponding author)FZJ*

1988
Kernforschungsanlage Jülich, Verlag Jülich

Jülich : Kernforschungsanlage Jülich, Verlag, Berichte der Kernforschungsanlage Jülich 2210, III, 107 p. (1988)

Please use a persistent id in citations: http://hdl.handle.net/2128/18525

Report No.: Juel-2210

Abstract: Detailed investigations of surface- and adsorbate-induced binding-energy shifts of Ir, Pt and Au 4f$_{7/2}$ core-levels have been carried out using photoemission with either synchrotron or Y M${\zeta}$-radiation (132.3 eV). Spectra recorded from clean (110)-1x2 surfaces show single surface peaks shifted to lower binding energy relative to the bulk peaks. These results are discussed in light of recent structural studies of the reconstructed (110) surfaces. Not only the surface core-level shifts, but also the intensity ratios of surface to bulk contributions in the 4f spectra of clean Au(110) and Pt(110) surfaces vary with temperature between 500 K and 750 K for Au and between 850 K and 1050 K for Pt. Outside these regions the shifts and intensity ratios remain nearly constant. We conclude that there are structural changes in both surfaces in the respective regions, which we identify as order-disorder transitions. The transition temperature for Au(110) is 620±50 K, in close agreement with other published values for this surface, whereas for Pt(110) the transition temperature is determined at 940±50 K for the first time. Another structural change is observed after cooling the Pt and Ir sample in ambient CO. The reduced surface to bulk intensity ratios with respect to the clean (110)-1x2 surfaces indicate that the reconstruction is lifted, because the 1x1 surfaces have less surface atoms. All adsorbates considered here (CO, O$_{2}$, H and K on Pt, K and CO on Au, CO on Ir) gave rise to an increased 4f$_{7/2}$ binding energy of the surface with respect to the clean surface. These adsorption-induced surface core-level shifts cannot be rationalized in terms of charge transfer between adsorbate and substrate, neither in amount nor even in direction. It is shown that final state effects in the photoemission process are responsible for this missing correlation. On the other hand all adsorption-induced shifts correlate with thermodynamic data in the framework of a Born-Haber cycle. It is demonstrated that the Y M$\zeta$ is also very usefull in the spectroscopy of adsorbate niveaus with binding energies of less than 20 eV, for example the K 3p niveau or the 4$\sigma$, 5$\sigma$ and 1$\pi$ orbitals of CO. The spectroscopy of the latter ones showed an adsorption of CO on Au(110) at 120 K.

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